Start from the percentage-of-retail bands
Resale value is expressed as a share of the original retail price, and every category and tier has its own band.
A durable mid-tier garment typically clears at 25–45% of retail. That is the working band for most of a wardrobe: solid pieces from known makers, bought at full price and worn with care.
A discontinued piece from a sought-after label can hold 80–100%, because the buyer cannot order it new at any price. Scarcity, not sentiment, lifts a listing out of the mid-tier band.
Category pulls hard inside the bands. Denim and outerwear hold value better than logo-heavy jersey, and the gap widens sharply below good condition — a fair-condition printed tee falls much further than a fair-condition denim jacket.